Telegraph system



Fell 9', 1943' c. A. DAHLBOM Erm. 253102.79

TELEGRAPH SYSTEM Filed June 6, l194:1 6 Sheets-Shet 1 WJM- mmf/50M /NVENTORS- HaHa-RN ATTORNEY Fell 9, 1943- c. A. DAHLBoM Erm. 2,310,279 l I TELEGRAPH SYSTEM Filed June 5f, 1941 6 SheebS-Sheet 2 .mmm YNHK ATTORNEY c. A. DAHLBOM ETAL 2,310,279

l TE1`.EGR.^.PH SYSTEM Filed June 6, 194:1 6 Sheets-Sheet 3 Feb. 9,. 1943.

MDM

c. A. DAHLBOM ET'AL 2,310,279

TELEGRAPH 'SYSTEM Fiied June` 6, 1941 6 sheets-sheet 4 l Feb. 9, 1943.

Feb. 9, 1943. Q A DAHLBOM ETAL 2,310,279

TELEGRAPH SYSTEM h Filed June 6,"1941 6 Sheets-Sheet .E -l

Feb. 9, 1943. c. A. DAI-H BOMl ETAL 2,310,279

TELEGRAPH SYSTEM Filed June 6, 1941' 6 Sheets-Sheet 6 ATTO/MEV Patented Feb. 9, 1943 UNITED STA :fi

aefogzve rnLEenAPi-r sYsrnM 'man eorporation of New York Application June 6, 1941, Serial No. 396,818 f 13 Claims. (Cl. 178-2) This invention relates to telegraph transmission systems.

An object of the invention is to provide improved transmission in two-Way telegraph systems, and in particular to provide transmission means and circuits which are less susceptible to distortion or needless adjustment or both on account of battery variations or variations in the characteristics of the line circuit, Whether the variations be caused by capacity, inductance, leakage, or diierence in ground potential at the terminals of the system.

Heretofore, in telegraph systems various types of circuits for transmitting messages were employed. Among these types are the neutral system, the one-Way polar system, the two-path polar system, duplex systems and polarential systems. A .brief description of the one-way polar and polarential systems will aid an understanding of the present invention.

One type of one-Way polar system which permits transmission of messages in one Way only, employs at the sending end of the line two batteries, one of each polarity, and at the receiving end of the line there is no battery, that is, the line is connected to a ground connection. When signals are being transmitted for the marking condition, one polarity of battery is connected to the line and for the spacing condition the other polarity of battery of the same magnitude is connected to the line. As a result, the currents for the marking and spacing conditions are of equal magnitude but opposite in direction, thereby producing a symmetrical Wave as regards marks and spaces At the receiving end of the line a polar relay without an external bias is employed and the operation of this relay is governed by the polarity of current which is transmitted from the sending station. This principle of operation is called polar, and it has the advantage over the open-and-closed principle in that it is practically unaffected by battery variations or variations in the characteristics of the line.

Grounded telegraph circuits are sensitive to changes in the weather, since those changes bring about variations in line leakage and line resistance. Where telegraph relays are located at subscribers premises or unattended remotely situated stations, frequent readjustment is impractical; to avoid it, the polarential method was developed. The polarenial method operates in one direction on diierences in current and in the other direction on reversals of cur-'5S rent. It includes two types of circuits; one type -A which is shown in Fig. 1 of U. S. Patent 2,131,870 granted to W. W. Cramer on October 4, 1938, and minimizes the eiect of variations in line resistance;- the other, type-B, Which is shown in Fig. 2 of the Cramer patent, supra, and in Figs. 1 and 2 of U. S. Patent 2,136,984 granted to C. W. Smith on November 15, 1938, and also in U. S. Patents 2,133,380 and 2,140,673, respecf tively, granted to R. W. Deardorff on October 18, 1938, and M. L. Greene et. al. on December 20, 1938, greatly minimizes the effect of variation in line leakage. In the type-A system the battery voltages at each end of the line are chosen so that the current in the line, although same magnitude for marking and, spacing, and

a given leakage at the middle point of the line Will, therefore, cause current to ground Which is the same for marking and spacing and hence the change in the receiving relay current will be the same for these two conditions. The polarential systems are used only on circuits that require transmission of signals in one direction at a time.

Others may have dened specific examples of such systems in other terms or may have included specific characteristics of speciiic ekamples of such systems in denitions of suchv speciiic examples.

According to the present invention a polar sending-diierential receiving telegraph repeater circuit is connected to a polar receiving-dinerential sending telegraph repeater by a three-Wire trunk circuit,`one Wire is employed in a one-Way polar system for transmitting message signals in one direction, the second wire is used in a type- B polarential system for transmitting message signals in the opposite direction, and the third Wire is employed for neutralizing voltages induced in either of the systems, from ground potentials or other extraneous sources. The trunk circuit may be arranged for half duplex or full duplex operation as desired.

A feature of the present invention is a duplex system in which transmission in either direction is independent of the leakage resistance of either line to ground.

Another feature is that only a single source of potential is required at one termination of the circuit.

Other objects and features will be noted in the following detailed description taken in conjunction with the accompanying drawings, of which:

Fig. l shows Figs. 2, 3 and 4 in diagrammatic form;

Figs. 1A and 1C show a modification of Fig. 1 wherein a local subscribers loop is connected in place of a toll line extension circuit at each end of the system;

Figs. 1B and 1D show a. modification of Fig. 1 wherein a hub circuit arranged for inverse neutral operation is connected in place of a toll line extension circuit at each end of the system;

Fig. 2 shows in block form a toll line subscriber station and in schematic form a toll line extension repeater interconnecting the toll line subscriber station and the repeater of Fig. 3;

Fig. 2A shows in block form the local subscriber station of Fig. 1A connected in place of the toll line extension repeater, to the repeater of Fig. 3;

Fig 2B shows in block form a hub circuit arranged for inverse neutral operation, connected in place of the toll line extension repeater, to the repeater of Fig. 3;

Fig. 3 shows in schematic form a polar sending-diierential-receiving repeater circuit designed for half duplex operation and arranged to be connected at one end to either a toll line station through the toll line extension repeater (Fig. 2), a local subscribers set (Fig. 2A), or an inverse neutral repeater circuit (Fig. 2B), and at the other end to the three-wire trunk circuit;

Fig. 4 shows in schematic form a polar receiving-differential-sending repeater circuit designed for half duplex operation and connected at one end to the three-wire trunk circuit and at the other end to another toll line subscriber station through a toll line extension repeater it being also shown for connection at the other end to either of the modifications (Figs. 4A and 4B) of the termination of Fig. 4;

Fig. 4A shows a modification of Fig. 4 wherein the toll line extension circuit is replaced with a local subscribers loop which is connected directly to the polar receiving-differential-sending repeater;

Fig. 4B shows a modification of Fig. 4 wherein the toll line extension circuit of Fig. 4 is replaced with the hub circuit arranged for inverse neutral operation;

Fig. 5 is a relative arrangement of Figs. 2, 3 and 4;

Fig. 6 shows in schematic form a polar sending-differential-receiving repeater circuit arranged for full duplex balanced loop operation;

Fig. 6A is a. modification of Fig. 6 whereof its jack terminating end is arranged for inverse neutral repeater operation required for connection to a hub circuit;

Fig. 7 shows in schematic form the polar receiving-diiferential-sending repeater circuit arranged for full duplex balanced loop for double polarity operation;

Fig. 7A is a. modification of Fig. 7 arranged for full duplex balanced loops for inverse neutral repeater operation required for connection to a hub circuit; and

Fig. 8 is the relative arrangement of Figs. 6 and 7.

A polar sending-differential receiving repeater may be dened as one which receives in one direction differential signals, that is by using differences in current owing in one direction and sends in the other direction, polar signals, that is, by using reversals in current, such types of repeaters being shown in Figs. 3 and 6. A polar receiving-differential sending repeater is one which receives in one direction polar signals, or reversals in current, and sends in the other direction differential signals, that is, the differences in current flowing in one direction, such types of repeater being shown in the left-hand portion of Fig. 4 and in Figs. 7 and 7A. The differences in current flowing in one direction means currents having different amplitudes of effective values but of the same polarity.

Referring to Fig. 1, block |0| represents an outlying subscriber station circuit connected by line |02 to a toll line extension repeater circuit |63 which in turn is connected by line |04 to the toll line repeater |05 also identied herein as a polar sending-differential-receiving repeater. The toll line repeater |05 is connected over a toll line |06 to another toll line repeater |01 also identified herein as a polar receiving-differential-sending repeater, at a distant point. The toll line repeater |01 may be connected by line |08, |08 or |68" to a toll line extension repeater |09, an outlying subscriber station or an inverse neutral repeater |09 as indicated. The repeater |09 is connected in the line circuit ||0 of an outlying subscribers station Outlying subscriber stations such as those designated |0| and are located at a considerable distance from the toll line repeater offices. Subscribers loop circuits |0| and are p-rovided for those stations which are located at comparatively short distances from the toll line repeater offices. Inverse neutral repeaters |03 and |09 may be connected to a subscriber loop or to another toll line. A description of the inverse neutral repeater circuits may be had by reference to United States Patents 2,056,277 and 2,069,251 respectively granted to F. S. Kinkead on October 6, 1936, and February 2, 1937. Each of the above-mentioned arrangements will be referred to hereinafter as the subscriber circuit.

Figs. 2, 3 and 4 represent a system arranged for half duplex operation and Figs. 6 and 7 represent the system arranged for full duplex operation.

The following description is divided into two parts, one for describing the half duplex operation and the other, the full duplex operation. Each part is subdivided into a general and a detailed description, the detailed description of each part including the method of operation. Also, provision is made herein for the use of a third wire in the two-path trunk circuits respectively arranged for full duplex and half duplex operation, the third wire or conductor serving to neutralize in the other two wires ground potentials and voltage interference induced from extraneous sources. In both the full duplex and half duplex systems the transmission from one toll line repeater to another is on a one-way polar basis, and transmission in the opposite direction is on a differential basis, that is, with differential signals. In both systems supervision is on a full duplex basis over a pair of telegraph lines but it has not been herein described because it 7:5.- forms no part of the present invention.

HALF DUPLEX OPERATION GENERAL DESCRIPTION Polar sending-diferentz'al-receiving repeater Fig. 3

Tho polar sending repeater, as shown in Fig. 3, is designed to operate between a toll line ex-V tension repeater TLX, shown in Fig. 2, and a toll line repeater circuit extending to a distant polar receiving repeater ofce shown in Fig. 4. The polar sending repeater comprises polarized send relay 30| and polarized receive relay 302.

Send relay 30| repeats the signals received from the toll line extension repeater TLX to send conductor 303 on a polar basis, that is, by current reversals, through the noise suppressor comprising resistances 306 and 301 and retardation coil 308, and the line equalizing, or shaping, network comprising retardation coil 309, condenser 3|0 and resistance 325. The send conductor divides at a mid-tap connection on the two windings of retardation coil 309, one path extending through the left-hand winding to condenser 3|0, resistance 325 to ground, and the other extending through the right-hand winding to trunk conductor 3| A potentionmeter comprising rheostat 312 and resistance 305 is provided to reduce the voltage applied to the line.

Differential signals incoming from the differential sending repeater at the distant end of the line are received in a circuit traceable over line conductor 3|2, through winding No. 5 of polarized receive relay 3| 3, conductors 341 and 3|4, keys 356 to 359 in their normal positions 3|5 and conductor 3|6, key 3|1 to grounded negative 130-volt battery 3|8. Relay 3|3, upon responding to the incoming signals, repeats them as polar signals in a `circuit traceable over receive conductor 3|9, through wave shaper 320, through the lower windings, in series, of polarized supervisory relay 330 and polarized auxiliary receive relay 302 to ground. Auxiliary receive relay 302 repeats the signals as polar signals over conductors 32| and 203 to the toll line extension repeater TLX wherein the signals are repeated to subscriber line 20| as current and no current impulses. The output of relay 302 is traceable from grounded positive or grounded negative 13G-volt battery 33| or 332, depending on whether the signal impulse is of a spacing or a marking type, spacing or marking contact and armature of relay 302, conductor 32|, then through the upper and lower windings, in parallel, of polarized relays 30| and 325, in series, one path extending over conductor 203, and the other over an artificial line 314 to ground. The windings of each of relays 30| and 325 are differentially arranged with respect to each other and therefore relays 30| and 325 do not respond to signals received from the armature of relay 302. Relay 325 is for supervisory purposes. 'Ihe receive line circuit comprising conductor 3|2 is arranged to provide good transmission with large variable amounts of line leakage present. Transmission over line conductor 3|| to the distant repeater oflice is on a one-way polar basis and is therefore not aiected in this direction by line leakage.

Partial neutralization' of ground potential, cross-nre and other induced voltage interferences is accomplished by the use of a third conductor 322 extending between the toll line repeater shown in Fig. 3 and the toll line repeater shown in Fig. 4 at the distant oiiice. The third conductor 322 vis connected through winding No.3 of receive relay 3 I3 to ground, and at the distant of- :ce -through the lower winding of receive relay 40| to ground so that it is subjected to the same induced voltages as both conductors 3| and 3|2, whichv are respectively connected to windings on relays 3|3 and 40|, said two windings on each of the relays being arranged in differential relation. Consequently, the third conductor suiciently neutralizes the effect of induced voltage interferences in either 'of the receive relays 3|3 and 40| to permit satisfactory transmission in either direction. Conductor 323 serves as an articial line for conductor 322.

An adjustable resistance 352 is provide-d for balancing the telegraph trunk conductor 3 2 connected to the repeater. When a balance is obtained between trunk conductor 3 2 and articial line 324, the differential eect of the current in windings Nos. 4 and 5 of relay 3|3, respectively connected in the circuit of trunk conductor 3|2 and the circuit of artificial line 324, is zero, particularly when the distant end of trunk conductor 3|2 is in a marking condition. The balancing network consists of resistance 352 and condenser 353. A duplicate set of balancing equipment is provided for use when a three-conductor trunk is used as shown in the drawings. The balancing network for three-conductor operation consists of resistance 354 and condenser 355. In other words, the balancing network connected to articial line 324 is used for balancing trunk conductor 3|2 forv two-conductor operation, while the balancing network connected to artificial line 323 is used for the neutralizing, or third, conductor. A biasing winding No.`1 is also provided on relay 3|3 to compensate for the directlcurrent owing in winding No. 4 to insure proper operation of receive relay 3|3.

Apex keys Five apex keys are provided to control the resistance in the circuits of trunk conductor 3|2 and third conductor 322. Each of these keys is arranged to affect the resistance of each of the apex circuits alike. The apex keys are of the locking type, preferably arranged to be operated with a turn-button top. Key 35S controls resistance 36| in the circuit of trunk conductor 3 I2 and resistance 366 in the Vcircuit of third conductor 322. In like manner, keys 351, 358, 359 and360, respectively,veontrol the four remaining pairs of resistances, as shown, resistances 362, 363, 364 and 365 `being respectively paired with resistances 361, 368, 369 and 310.

Balance keys Balance key 3|1 is non-locking and is of the push-button type. It is provided to reverse the apex Voltage when the repeater is being lined up on the trunk conductor to which the repeater is connected.

Monitoring Provision is made for common monitoring with an indicating milliammeter arranged to be patched to any one of five jacks connected in the repeater circuit. The indicating milliammeter serves for observation of signals and line balance under diierent conditions. This meter is of the single-coil type, has a double indicating scale with a zer0,midpoint and is adapted to operate in opposite directions in accordance with f the direction of the operating current. This device is known; see United States Patent 1,809,026 granted to G. C. Cummings on June 6, 1931.

For the purpose of lining up of the repeater it will be assumed that connections have been made to a subscriber station circuit at one end and to a three-conductor trunk circuit extending to the trunk repeater at the distant oilce.

Jack 34| is provided in series with said trunk conductor 3|| for checking the line current and to permit observation of signals transmitted over the line. The reading indicated on the milliammeter patched to the send trunk conductor 3|| is the actual line current.

Jack 345 is provided in series with the receive trunk conductor 3|2 for checking the line current and to permit observation of signals received over the line. The reading on the milliammeter patched to receive trunk conductor 3|2 is likewise the actual line current.

Balance jack 342 is provided for connecting the milliammeter to indicate the differential current between receive trunk conductor 3|2 and its associated articial line 324. The reading on the milliammeter is the actual differential current. After necessary adjustments of resistances, a normal balance may be obtained.

Balance jack 343 is provided for connecting the milliammeter to indicate the interference on the neutralizing, or third, conductor 322 for comparison with the interference on the receive trunk conductor 3|2. After the necessary adjustments of resistances, a similar normal balance may be obtained.

Bias jack 344 is provided for connecting the milliammeter to the biasing circuit so that the biasing current in winding No. 1 of receive relay 3|3 may be adjusted to the proper value. The shunting resistance 31| across bias jack 344 is so proportioned that the value of current indicated on the milliammeter when the biasing current is properly set will be equal to the current obtained with the milliammeter patched to balance jack 342 when a spacing signal is transmitted from the repeater at the distant olce.

These tests with the milliammeter must be made in conjunction with the attendant at the distant office, who sends steady marking and steady spacing signals, the steady signals being produced by locking in the letter R signal in the teletypewriter at the distant end of the trunk and adjusting the biasing current and winding No. 1 of receive relay 3|3 to obtain a maximum margin range on a monitoring teletypewriter in good adjustment, connected to a loop circuit at the operators switchboard.

Noise suppressor A noise suppressor consisting of retardation coil 308 and resistance elements 306 and 301 is provided in series with send conductor 303.

Contact protection Contact protection is provided across the contacts of relays 30|, 302 and 3|3. The condensers and resistance elements connected across the contacts of each of these relays prevent the occurrence of sparks at the gaps.

Send Zine potentiometer Send line potentiometer consisting of rheostat 312 connected to the apex of the send line of the repeater and resistance 305 connected to ground are provided so that the current in send trunk conductor 3|| may be adjusted to say $35 milliammeters when the repeater voltages are volts.

Bias potentiometer Bias potentiometer 313 is provided in the biasing circuit of receive relay 3|3 so that the current in this circuit may be adjusted to the proper value.

Receive relay Receive relay 3|3 is provided for receiving signals from the distant end and retransmitting them to the subscribers circuit. The relay is equipped with ve windings which are arranged for connection in ve circuits. One winding, No. 5, is connected to receive trunk conductor 3|2; another, No. 4, is connected in the artificial line 324; still another, No. 3, is connected in third conductor 322; still another, No. 2, is connected in the artificial line 323 for third conductor 322; and still another, No. 1, is connected in the biasing circuit which is required for type B polarential operation.

Auxiliary receive relay Auxiliary receive relay 302, responds to the signals retransmitted by relay 3|3 and repeats them over a circuit extending through the windings of relays 30| and 325 and over two parallel paths, one along conductor 203 to the subscribers line and other to ground through articial line 314.

Send relay Send relay 30| is provided for receiving signals from the subscribers line and to retransmit them to send trunk conductor 3| This relay is equipped with two windings differentially arranged with respect to each other, one winding being connected in series with conductor 203 of the loop circuit and the other in series with artificial line 314. Relays 30| and 325 do not respond to the signals repeated by auxiliary receive relay 302, because of their dilerential windings.

Eqaaliaing networks An equalizing network is provided for the send conductor 3|| as hereinbefore mentioned, it being adjusted for optimum transmission to the repeater at the distant oce. An equalizing network is provided for receive conductor 3|2 comprising condenser 353 which is adjusted for optimum transmission. Condenser 355 is a duplicate of condenser 353 and is provided for the neutralizing, or third, conductor 322 in order to maintain a duplicate balance for receive conductor 3|2 and neutralizing conductor 322.

Polar receiving-diferential sending repeater Fig. 4

This circuit is designed to provide a half duplex terminal repeater operating over two con ductor lines with provisions for partial neutralization of line interference by use of a third line conductor. Transmission from the polar sending repeater at a distant oce is on a one-way polar basis and the repeater is designed, therefore, to receive polar signals from the trunk circuit and to repeat the signals to a subscribers loop or to a toll line extension repeater, for transmission to a subscribers set. The repeater is designed to receive signals from a subscribers loop or from a toll line extension repeater and to repeat the signals to the trunk circuit as the differential sending end lof the system. The repeater will operate without'` transmission losses due to line leakage, since inward transmission is polar and readjustnient may take care of the other deviation. In order to compensate for ground potentials and induced voltage interferences provision is likewise made at this repeater for using the third conductor to serve as a neutralizing circuit.

Signals transmitted from subscribers station 402 or 402 are received over conductor 4|6 by polarized send relay 4|3 which operates and thereby repeats the signals over conductor 429, noise suppressor and wave shaper, trunk conductor 3|2 to the trunk repeater at the distant office. The signals thus transmitted to the distant oice are ground and positive 13G-volt battery for the polarential sending end of the type B polarential system.

The polar signals received from the distant oifice are repeated by the polarized receive relay 40| to a polarized auxiliary receive relay 401 which, in turn, repeats the signals over conductor M6 to either of the subscribers stations 402 or 402.

subscribers station 402 is located at a considerable distance from the office and therefore requires a toll line extension repeater interconnecting conductors 4|6 and 423. station 402' is located at a comparatively short distan-ce from the office and is therefore connected directly to the repeater at the ofice. subscribers station 402 is of the ordinary subscribers loop type whereas subscribers station 402 is of the type disclosed in Fig. 1 of U. S. Patent 2,143,000 granted to W. W. Cramer et alv on January 10, 1939.

Partial neutralization of ground potential, cross-lire and other induced voltage interferences is accomplished by use of the third conductor 322 between the distant oiTice and this office, which is subjected to the same exposures as the operating .path of conductors 3|| and 3|2. Winding No.A 3 on receiving relay 3|3 at the distant ofce and the lower winding of relay 40| at this ofce are connected together by this third conductor 322.

Transmission to the repeater at the distant office has been improved by the use of aline Wave shaper comprising retardation coil `433 and condenser 434 which are adjusted for optimum transmission over the particular trunk circuit used. This wave shaper serves as an equalizing net- Work for the telegraph line circuit and, in addition, helps to decrease telegraph thump to a satisfactory level.

Send relay Send relay 4|3 is `provided for receiving sigf nals over conductor 4I6 and retransmitting them over send trunk conductor 3|2 to the distant ofce. Relay 4|3 is equipped with two windings, one of which is connected in series with conductor 4|6 which may extend either through the toll line extension circuit to subscribers station 402 or directly to subscribers station 402. The other winding of relay 4|3 is `connected in series with the articial line terminating at ground connection 4 I 5.

Receive relay Polarized receive relay 40| is provided for receiving signals from the distant oiice and retransmitting them over a circuit extending from ground 440 or battery 403 depending upon which of its two contacts the armature of relay 40| is in engagement with at the time the circuit is closed over conductor 404 through the winding subscribers of polarized relay 406, the lower winding of pol-arized auxiliary receive relay 401 to a potentiometer connected between positive 13G-volt .battery 403 and ground 446. Relay 40| is equipped with two windings, one of which is .connected to receive trunk .conductor 3| and receives signals incoming from the distant olce, 'and the other, is connected to third conductor 322 and is provided for neutralizing induced voltage interferences.

Auxiliary receive relay Polarized receive relay 401 is provided for receiving signals repeated by receive relay 40| and retransmitting them to conductor 4|6. Relay 401 is equipped with two windings, one of which, as hereinbefore stated, receives the signals repeated by relay 40| and the other is a biasing winding for holding relay 401 in its right hand, cr marking, position when transmission'is toward the distant oiiice. f

Supervisory relay Polarized relay 4 4, -both windings of which are respectively connected in series with those of send relay 4|3, and polarized relay 400, the winding of which is connected in series with the lower, or signal, winding of auxiliary receive relay 401, are for supervisory purposes -but inasmuch as supervision forms no part of the present invention no further description is deemed necessary.

Noise suppressor A noise suppressor consisting of retardation coil 432 and resistances 430 and 43| is provided in series with send trunk conductor 3|2.

Equalizing network An equalizing network is provided for send trunk conductor 3|2 and comprises retardation coil 433, resistance 431 and condenser 434. The resistance and the condenser are adjusted `for optimum transmission toward the repeater at the distant oftlce.

Contact protection Contact protection is provided across the contacts of send relay 4|3 and receive relay 40|.

Anti-kickoff network A network 439 is provided to prevent kickoi when relay 401 transmits signals to the Vsubscriber loop.

Toll line extension repeater circuit Shaping networks Several wave shapers are provided for improving the signals incoming over` conductor 4|6. Satisfactory wave Shapers are shunted condenser 426 and network 420. Network 420 comprises resistance 440, inductances 44| and 442 and resistance 444, the latter resistance shunting resistance 440 and indu-ctance 44 I.

Contact protection Contact protection is provided across the contacts of relays 4|1 and 4|9.

Supervisory relay Polarized relay 42| is provided for furnishing supervision over signals received from the subscriber station 402 but, as hereinafter stated, a description of the supervisory features is not deemed necessary.

DETAILED DESCRIPTION METHOD oF OPERATION Transmission from the toll subscriber station at polar sending end to toll subscriber station at polar receiving end When a connection is established for transmission from toll subscriber station 20| to toll subscriber station 402, signals are received in a circuit extending over conducto-r 202, through the upper winding, in series, of polarized relays 204 and 205, shaping network 206, armature and marking, or left-hand, contact of polarized relay 201 to ground. Relays 204 and 205 respond to these signals. Relay 205 is for a supervisory relay and may be used to control signal circuits, lamps or other devices not shown. Relay 204, upon responding to the signals, repeats them by means of its spacing'and its marking contacts which are, respectively, connected to grounded positive 130- volt battery 208 and ground connection 209, and its operating armature in a circuit extending over conductor 2|0, through the upper and the lower windings, in parallel, of relay 201, the path of the lower winding extending to a Iixed potentiometer connected between grounded positive 130- volt battery 208 and ground connection 209, and the path of the upper winding extending over wave shaper 2| I, conductor 203, through the upper windings, in series, of polarized relays 325 and 30|, conductor 32|, armature and marking, or right-hand, contact of auxiliary relay 302 to grounded negative 13D-volt battery 332. Signal current impulses incoming over lead 203 from the toll line extension repeater shown in Fig. 2 overcome the biasing current in the lower winding of relay 30| so that the relay becomes responsive to the incoming signals. Connected in series with relay 30| is polarized relay 325 which is used for supervisory purposes not described herein.

The incoming polar signals are repeated by means of the spacing and marking contacts respectively connected to grounded positive 130- volt battery 326 and grounded negative 13D-volt battery 321 and the operating armature of relay 30| in a circuit extending over conductor 303, potentiometer rheostat 312, through the noise-killer, and the equalizing network trunk conductor 3| through the upper winding of polarized receive relay 40| to ground. Any voltage from an extraneous source induced in trunk conductor 3|| is likewise induced in third conductor 322. Conductor 3|| extends through the upper winding of receive relay 40| and third conductor 322 extends through the lower winding of relay 40| and therefore the eiect of the induced voltage in conductor 3H is neutralized by the induced voltage of equal magnitude in conductor 322, since both windings are differentially wound with respect to each other. The transmitted polar signals are, during transmission, unaffected by battery variations or variations in the characteristics of the trunk conductors 303 and 3| Receive relay 40| responds to the message signals incoming over trunk conductor 3|| and repeats them by means of the spacing and marking contacts respectively connected to grounded posi- 5 tive 13G-volt battery 403 and ground 446, depending upon the contact engaged at the time by the armature of relay 40|, and the operating armature of the relay, in a circuit extending over conductor 404, through the shaping network 405, through the Winding of polarized supervisory relay 406, through the lower winding of polarized auxiliary receive relay 401 to a potentiometer between grounded positive 130-volt battery 403 or ground 440. Auxiliary receive relay 401 is held in the position shown, namely, marking, when transmission is toward the polar sending repeater of fice as hereinbefore stated.

Auxiliary receive relay 401 responds to the signals repeated by receive relay 40| and repeats the signals by means of the spacing and the marking contacts respectively connected to ground 408 and grounded positive 13G-volt battery 409 and the operating armature oi relay 401, in a circuit extending over retardation coil 4| 0, conductor 4 2, through the upper and the lower windings, in

parallel, of polarized relays 4| 3 and 4|4, connected in series, over two paths, one extending through the articial line to ground 4I5 and the other over toll conductor 4|6 to the repeater in the toll line extension circuit. The windings of relays 4|3 and 4|4 are differentially wound with respect to each other and are normally held in their marking, or right-hand, positions as shown and do not respond to signals repeated as current and no current impulses by relay 401.

The signals repeated by relay 401 over trunk conductor 4|6, through the upper winding of polarized send relay 4|1, conductor 4| 8, armature and marking, or right-hand, contact of polarized relay 4|9 to ground connection 424 to cause relay 4|1 to operate. Relay 4|1, upon responding to the incoming signals, repeats them, without change, except that due to attenuation in a circuit extending over operating armature of relay 4|1, shaping network 420, through the upper and lower windings, in parallel, of polarized relays 42| and 4|9 connected in series, the path through the upper winding extending over conductor 423 to the outlying subscriber station 402 whereat the signals are recorded, and the path through the lower winding extending through the artificial line to ground 441. Relays 42| and 4|9 do not operate at this time. Subscriber station 402 may be so equipped as to furnish both attended and unattended service as disclosed in Fig. 1 of United States Patent 2,143,000, supra.

In the event that conductor 456 is connected through a local subscriber loop to subscriber station 402', the toll line extension repeater circuit is omitted and conductor 4 6 is connected directly to the subscriber station as is disclosed at the right side of Fig. 5 of the United States Patent 2,143,000 supra, wherein conductors R and T, respectively, correspond to conductors 4|6 and the dash line shown connected to ground at connection 422.

Likewise, if conductor 4|6 is connected to an inverse neutral repeater 402 the toll line extension repeater circuit is omitted and the conductor 4|6 may be connected directly to any of the inverse neutral repeater arrangements disclosed in United States Patents 2,056,277 and 2,069,251, respectively granted to F. S. Kinkead et al. on October 6, 1936, and F. S. Kinkead on February 2, 1937.

Transmission from a toll subscriber station at polar receiving end to toll subscriber station at polar sending end When a connection is established for transmission from the outlying, or toll, subscriber station '402, to toll subscriber station 20|, signals are received in a circuit extending over conductor 423, through the upper windings, in series, of relays 4|9 and 42|, shaping network -420, armature and marking, or right-hand, contact of relay 4|1 to ground. Relays 4| 3 and 42| respond to these signals. Relay 42| is for supervisory purposes and its operation and eiect is not described herein. Relay 4|9, upon responding to the signals, repeats them by means of its spacing and its marking contacts which are respectively connected to grounded positive 130-volt battery 425 and ground connection 424, and its operating armature in a circuit extending over conductor 4| 8, through the upper and the lower windings, in parallel, of relay 4|1, the path of the lower winding extending to a xed potentiometer connected between grounded positive 13G-volt battery 425 and ground connection 424, and the path of the upper winding extending over wave shaper 426, conductor 4|6, through the upper windings, in series, of relays 4|4 and 4|3, conductor 4|2, retardation coil 4|0, armature and marking, or right-hand, contact of relay 401 to a xed potentiometer connected between grounded positive 13G-volt battery 409 and ground connection 4|5, or to ground connection 403, depending upon the nature of the received signal. Send relay 4|3 operates in response to the signals. Supervisory relay 4|4 likewise responds but the effects of its operation are not described herein.

Send relay 4|3, upon responding to the signals received from conductor 4|6, repeats the signals by means of its spacing and its marking contacts which are respectively connected to grounded positive 13G-volt battery 421 and ground connection 428, and its operating armature, in a circuit traceable over conductor 429, the noise suppressor and the wave shaper, trunk conductor 3|2, through winding No. 5 of receive relay 3|3, conductors 341 and 3|4, through the normally closed keys 356 to 359, in series, conductor 3|6, key 3|1 to grounded negative 13G-volt battery 3|8. One or more resistances 33| to 365 may be added as desired by operating their respectively associated keys 356 to 360, whereby corresponding resistances 366 to 310 are included in the circuit of third conductor 322.

Relay I3|3 responds to the differential signals incoming over trunk conductor 3|2, and thereby repeats them as polar signals by means of its spacing and its marking contacts which are respectively connected to grounded negative 130- volt battery 328 and grounded positive 13o-volt battery 329, and its armature, in a circuit traceable over conductor 3| 9, wave shaper 320, through the lower windings, in series, of relays 330 and 302 to ground. Relay 330 is for supervisory purposes, and its operation and eiect are not described herein inasmuch as, as hereinbefore stated, the supervisory features are no part of the present invention. Relay 302 responds to the signals received over conductor 3|9 and thereby repeats the polar signals by means of its spacing and its marking contacts which are respectively connected to grounded positive 13G-volt battery 33| and grounded negative 13D-bolt battery `332, andthe 4relay armature, in a circuit traceable over conductor 32|, through the upper and the 75 lower windings, in parallel, of relays 30| and 325 in series, the path of the lower windings extending to ground through an artificial line 314 and the path of the upper windings extending over conductor 203, shaping network 2| through the upper winding of relay 201, conductor 2|0, armature and marking, or left-hand, contact of relay 204 to ground connection 203. Relay 201 responds to the signals incoming over conductor 203 and repeats them, as signals of current and no current, in a circuit traceable over shaping network 206, through the upper and the lower windings, in parallel, of relays 205 and 204, in series, the path through the upper windings extending to the toll subscriber set 20| and the path through the lower windings extending to ground over an artificial line. Relay 205 is for supervisory purposes and relay 204 is the send relay, but neither operate in response to incoming signals because of the differential arrangement of their respective windings.

It will be noted that transmission from send relay 30|, over conductor 3| to receive relay 40| is of the one-way polar signal type which, as hereinbefore stated, requires no compensation for line leakage. The transmission in the opposite direction, that is, from send relay 4|3, over conductor 3|2, to receive relay 3|3 is of the differential type. The latter type uses as signals currents of markedly different amplitudes but of the same polarity and the above-mentioned circuit comprising conductor 312 requires adjustments principally by means of keys 356 to 359 and the aid of the attendant at the concentrating unit oice, but once the circuit is adjusted for the line leakage practically no further adjustments are necessary regardless of whether the weather is wet or dry.

FULL DUPLEX OPERATION General Description Polar sending-djerential receiving repeater Fig. 6

This circuit is designed to provide a full duplex telegraph repeater system comprising two conductor lines with provision for partial neutralization of line voltage interferences by use of a third conductor line. The local side of the repeater provides full duplex legs for balanced loop operation or for L8-volt inverse neutral operation. Losses from cross-fire, voltage interference and earth potential are partially eliminated by the use of the third conductor so long as the three conductors of the trunk remain balanced.

Transmission from the repeater shown in Fig. 6 to the repeater shown in Fig. 7 is on a oneway polar signal basis. Transmission in the opposite direction is on a differential basis. Ihe repeater shown in Fig. 6 operates on a full duplex basis.

Five jacks are provided for patching an indicating milliammeter to measure the signal current in the trunk conductors and the biasing cir- 4cuit for receiving relay 6|6 and to indicate the differential current in the receive relay EIB. 'Ihe indicating milliammeter is for observing signals and line balance under different conditions. This meter is of the same type as hereinbefore described, whichA is a single coil type and a scale with a zero mid-point and is adapted to operate in opposite directions in accordance with the direction of the operating current.

Apex keys Five apex keys are provided to control the resistance in the circuits of trunk vconductor 1 L9 and third conductor 120. Each of these keys is arranged to aect the resistance of each of the apex circuits alike. The apex keys are of the locking type, preferably arranged to be operated with a turn-button top. Key 652 controls resistance 662 of third conductor 1211. VIn like manner keys 653, 654, 655 and 6,56, respectively, control the four remaining pairs of resistances as shown, resistances 658, 6'59, 660 and 66| being, respectively, paired with resistances 663, ,664, 665 and 666.

Balance keys Balance key 626 is non-locking and is of vthe push-button type. It is provided to reverse the apex voltage when the repeater is being lined up on the trunk conductor to which the repeater is connected. Balance key 661 is of ythe same type as key 620 and is provided to normally remove the battery from key 620 and thus be held Aoperated when key 620 is used when balancing the repeater.

Monitoring Provision is made for common monitoring with an indicating milliammeter arranged to be patched to any one of five jacks connected in the repeater circuit. 'The Vindicating ,milliammeter serves for observation of signals and line balance under diierent conditions. This met'er is of the single coil type, has a scale with a Zero midpoint and is adapted to operate in opposite directions in accordance with the vdirection of the operating current. This type is well known in the art as hereinbefore stated. It is used to facilitate adjustment and balance. The five jacks are as follows:

Jack 650 is provided in series with send trunk conductor 6|5 for checking the line current and to permit observation of the signals transmitted over the line. The reading indicated on the milliammeter is the actual line current.

Jack 65! is provided in series with receive trunk conductor 1|9 for checking the line current and to permit observation of signals received over the line, This reading likewise is the vactual line current.

Balance jack 665 is provided ior connecting the milliammeter to indicate the diierential current between received trunk conductor `7l9 and its associated artificial line 622. The reading on .the milliammeter is the actual differential I current.

Balance jack 610 is provided for connecting the milliammeter to indicate the interference-on the neutralizing, or third, conductor 120 for comparison with the interference on the received trunk conductor 1 i9. Y

Bias jack 61| is provided for connecting the milliammeter in the biasing circuit so that ,the bias current may be adjusted to the proper value. The shunting resistance 612 across bias jack '61| is so proportioned that the value of current indicated onthe milliammeter when the biasing current is properly set-will beequa-l to` thecurrent obtained with the meter patched to balance jack 659 when a spacing .signalis transmitted from the repeater at the distance oice.

Noise suppressor A noise suppressor consisting of retardation coil 6H and resistance elements-608 and 609 is provided in series with send conductor 6HL resistance 614.

Contact protection Contact protection is provided across the contacts of send relays 60| and 636 and across the contacts of receive relay 616. The condensers and resistance elements connected across the contacts of each of these relays prevent the occui-rence of sparking.

Leg circuit wave Shapers Wave shapers to ground are connected across conductors 640 and 645 to compensate for the armature travel time `of relay 643 transmitting to the leg circuit, The wave shaper connected Ato conductor 669 consists of condensers 613 and The wave shaper connected t0 conductor 645 consists of condenser 616 and resistance v615. Resistances 614 and 615 have equal value.

Potenttometers-Send Zine potentiometer Send line potentiometer comprising rheostat 621 connected in the apex of the send line of the repeater and resistance 6I0 connected from the apex to ground is provided so that the current in send trunk conductor SI5 may be adjusted to 135 milliamperes.

Balancing resistance potentiometers The balancing resistance potentiometers consist of two units, namely, 625 and 632 shown mounted on opposite sides of a ground connection. The potentiometers are used to obtain direct current balances in the artificial line circuit of the received trunk conductor 119, and the neutralizing, or third, conductor 120. For two-wire operation, that is where the third conductor is omitted, potentiometer 632 may also be omitted.

Bias potentiometer Bias 'potentiometer-696 is provided inthe biasing circuit of receive relay lSIB so that the current in this circuit may be adjusted to the proper value. Resistance .611 maybe strapped in or out of the circuit Vto extend the current range beyond the value obtained with the potentiometer.

Receive relay Receive relay 6|6 is provided forreceiving signals from the distant end of the line and retransmitting them to the local loop or leg multiple circuit at the operators switchboard. This relay is equipped with six windings which are arranged for connection in ve circuits. One winding, that is, No. 4, is connected tothe receive trunk conductor 1I9 as shown, and the second Winding, No. 3, is connected to the artificial line 622 which is used for balancing thereceived trunk conductor. The third and the fourth windings, Nos. 2 and 1, are respectively connected vto the third conductor 120, and artificial line 629, Vfor eiecting the desired neutralization of induced voltage interferences on the trunk conductors 119 and 6I5. The remaining two windings, Nos. 6 and 5, are connected in series and yare used lfor biasing therelay as required for type B polarential operation.

Send relay Send relay 68| is provided for receiving sig- -nals from the `local loop and to transmit them vas polar signals to send trunk conductor 615. yThis-relay is equipped with two windings; one winding is connected in series with conductor .S19 of the loop and resistance 619 and the other` is connected in series with an articial line comprising resistance element 680.

Send relay 636 is provided for receiving signals from conductor 640 to which is patched by means of jack 68| plug 662 of the operators cord circuit which is connected to a hub circuit at its other end. Relay 636 repeats the received signals, as polar signals to send conductor 639 which is an alternative conductor for conductor 666. Send -relay 636 is equipped with two windings. One winding is connected over conductor 640 to the hub circuit on one side and on the other side in series with resistances 683 and 684 to grounded liis-volt battery. Resistance 682 is shunted by condenser 685. The other winding of send relay 636 is connected in series with a biasing circuit comprising resistance 686 between ground and grounded Lifi-volt battery.

Receive relay (inverse neutral operation) Receive relay 643 is provided for receiving signais from receive relay 6| 6 which is shown in Fig. Glas relay 6|6, and to retransmit the signals to conductor 645 to a hub circuit connected to the opposite end of the cord circuit, plug 662 of which is patched to jack 68|. This assures uniform travel time from the contacts of the relay repeating signals over conductor 645. Relay 643 is equipped with one winding which is connected in series with resistances 6152 and 66| to the armature of receive relay 6|6.` Resistance 64| is shunted by condenser 681 for wave shaping purposes.

Networks An equalizing network is provided for the send conductor 6M comprising retardation coil 6|2, condenser 6|3, and resistance 688, the condenser and resistance being adjusted for optimum transmission to the repeater at the distant oli-ice. A line balancing network is provided for receive conductor H9, comprising condenser 623 and resistances 62a and 625 which are adjusted for optimum transmission. Condenser 630 and resistances 63| and 632 are a duplicate of condenser 623 and resistances 624 and 625 and is provided for the neutralizing, or third, conductor '|20 in order to maintain a duplicate balance for receive conductor 'H9 and neutralizing conductor 120.

Polar receiving-diyerentiaZ-sending repeater Fig. 7

Monitoring Jack '|35 is provided for patching a milliammeter to receive trunk conductor 'i 9 for measuring the line current. The reading indicated on the meter is the actual line current.

Noise suppressor A noise suppressor consisting of retardation coil 'H5 and resistances 'H3 and 'H4 is provided in series with the send conductor 1|9.

Contact protection ContactA protection is provided across the contacts oi send relay 10B and send relay 12| andy across the contact of receive relay |0|.

Leg circuit wave Shapers Wave shapers to ground are connected across conductors T36 and 35 to compensate for the armature travel time of relay |32 transmitting to the leg or hub circuit. The wave shaper connected to conductor `l36 comprises condenser '|38 and resistance The Wave Shaper connected to conductor i comprises condenser 14| and resistance lllil. Resistances 13 and |40 are oi' equal value.

Receive relay Receive relay 10| is provided for receiving signals from the distant ofce and retransmitting them to the local loop or leg multiple, or hub, circuit. Relay lill is equipped With two windings, one of which is connected to the receive conductor 6|5 and receives the signals incoming from the distant oice, and the other is connected to third conductor '|26 and is provided for neutralizing voltage interference.

Send relay Send relay W9 is provided for receiving signals over send conductor '|68 and retransmitting them over the send trunk conductor 'l I9 to the distant oice. Relay 169 is equipped with two windings, one of which is connected in series with resistance lili, send conductor |08 and the send conductor of the operated cord circuit to which plug '|01 is attached, and the other winding of which is connected in series with resistance l43 of the artiiicial line.

Send relay `|2| is provided for receiving signals from a hub circuit connected to send conductor '|36 over a cord associated with plug |24 and retransmitting them over send conductor '|22 `and send trunk conductor 'H9 to the distant oflice. Relay |'2| is equipped with two windings one of which is connected to send conductor '|36 and in series with resistances '|66 and '|45 to grounded negative 48-volt battery 733. Resistance 145 is shunted by condenser 166. 'Ihe other winding of relay 72| is connected in series with a biasing circuit comprising resistance 'M1 and grounded negative 48-volt battery '133.

Equalieing network An equalizing network is provided for send trunk conductor 'H9 and comprises retardation coil 1 il, condenser '|I8, and resistance 150. The condenser and the resistance are adjusted for optimum transmission toward the repeater at the distant ofce.

DETAILED DESCRIPTION METHOD or OPERATION Transmission from the polar sending repeater shown in Fig. 6 to the polar receiving repeater shown in Fig. 7

When a connection is established for transmission fro-m the local side or the polar sending repeater shown in Fig. 6 to a sub-scribers loop that may be connected at the repeater shown in Fig. 7, polarized send relay 60| receives the signals in a circuit traceable over plugv 602 patched to jack 603, through the lower winding of relay 60| to grounded positive 13G-volt battery. Relay 60| `which is normally in the position shown, due to a biasing current ilowing in a circuit traceable through the upper winding of the relay and through the articial line to ground, responds tothesignalsincoming from the operators teletypewriter or a subscribers loop circuit either of which may be connected to the switchboard cord circuit of plug 602. Relay 6M, upon responding to the incoming signals, repeats them as polar signals in a circuit traceable from grounded positive 13G-volt battery 664 or grounded negative 13S-volt battery 605, their respective spacing and marking contacts and the relay armature, conductor 666, potentiometer rheostat 661, noise suppressor, equalizing network, trunk conductor 6I 5, through the upper winding of polarized receive relay 16| to ground. Receive relay 10| responds to the signals repeated by send relay GSI and, upon responding, repeats the polar signals in a circuit traceable from grounded negative 13D-volt battery 162 and grounded positive 130- volt battery 163, their respective spacing and marking contacts in engagement with the associated armature of the relay, conductor 106, conductor 165, to the lower spring member of jack 166 at an attendants switchboard where the signals repeated by receive relay 16| are received at an attendants teletypewriter or transmitted to a substation as desired.

'Ihe transmission just described is on a one-way polar basis and is practically unalected by battery variations and variation in the characteristics of conductors 6I4 and 6I5.

Transmission from the differential sending repeater shown in Fig. 7 to the differential receiving repeater shown in Fig. 6

When signals are received from a local or a toll subscriber station they are impressed on a circuit traceable over plug 101 patched to jack 166, conductor 168, through the upper winding of polarized send relay 10S to grounded 13D-volt battery Normally when jack 106 is engaged, relay 169 is in the position shown due to the current owing through its upper winding and conductor 108. Relay 109 responds to the signals received over conductor 168 and, upon responding, repeats the signals as current and no current impulses in a circuit traceable from grounded positive 13G-volt battery 1I() and ground connection 1I I, their respectively associated spacing and marking contacts and the relay armature, conductor 1I2, noise suppressor, equalizing network, trunk conductor 1I9, through winding No. 4 of receive relay 6I6, conductors SI1 and EIS, through the upper normally closed contacts of keys 652 to 656 or through one or more of resistances 651 to 66 I depending upon which of control keys 652 to 656 are operated to opened positions at their Lipper contacts, conductor 6I9, non-locking push-button key 626 to grounded negative 13C-volt battery 62I. Resistances 662 to 666 which respectively correspond to resistances 651 to 66| in value, are included in the circuit of third conductor 126 in accordance with the operation of one or more of -keys 652 to 656 to opened positions at their lower contacts. Differentially arranged with trunk conductor 1I9 which is connected to winding No. 4 of relay 6I6 is articial line 622 connected to winding No. 3 of relay 6I6 to ground over two paths, one path including condenser 623 and the other path including resistance 624 and potentiometer rheostat 625.

Transmission over trunk conductor 1I9 towards the repeater shown in Fig. 6 is on a diierential basis.

Partial neutralization of ground potentials, cross-fire and other induced voltage interferences is accomplished by the use of third conductor 129 extending between the trunk repeater at this ofce (Fig. 7) and a trunk repeater at the distanct office (Fig. 6). The third conductor 126 is connected at the distant oiiice to a circuit extending through winding No. 2 of relay 66, conductors 626 and 621, through the normally closed lower contacts of keys 652 to 656 or one or more resistances 662 to 665 depending upon whether one or more of control keys 652 to 653 are operated, resistance 689 to ground connection 628. At this office, third conductor 126 is connected to the lower winding of receive relay 18| to ground so that it is subjected to the saine induced voltages as trunk conductors SI5 and 1 9 and consequently suiiciently neutralizes the eiiect of induced voltage interferences in either of receive relays 16| and 6I6 to permit satisfactory transmission, Conductor 629 serves as an artificial line for the third conductor 626 and comprises in one path to ground condenser 635 and in the other path to ground resistance 63| and potentiometer 632. A biasing circuit extends through the two windings Nos. 5 and 6 in series of relay SIB and is provided for biasing this relay.

Receive relay 6I6 responds to the signals received over trunk conductor 1I9 and, upon responding, repeats the signals on a polar basis in a circuit traceable from grounded negative 13C-volt battery 633 or grounded positive 130- volt battery 664, their respectively associated spacing and marking contacts and armature of the relay, conductor 635 to the lower spring of jack 663 to which plug 602 is patched for connecting a local subscriber station.

Figure 6A In Fig. 6A the terminating equipment for the repeater at the polar sending repeater oihce is shown for connection to multiple jacks at the switchboard whereby is furnished inverse neutral, or hub, circuit'l operations as disclosed in United VStates Patents 2,056,277 and 2,069,251, supra. Send relay 636 is normally held in the position shown by the biasing current in its upper winding. A line current will normally flow from grounded negative 13G-volt battery 631, marking, or right-hand, contact and armature of relay 636, conductor 639, potentiometer 601, noise suppressor and equalizing network, over trunk conductor SI5 as hereinbefore described. When a spacing impulse of the signal is received from the hub circuit by the application of ground at the local switchboard, and over conductor 640, relay 636 operates to its spacing, or left-hand, contact due to current flowing in the lower winding of the relay. Relay 636 in its spacing position, transmits current from grounded positive 13G-volt battery 638, spacing, or left-hand, contact and armature of relay 636, conductor 639, potentiometer 661, noise suppressor and equalizing network, trunk conductor 6 I4 as hereinbefore described. The signals repeated by send relay 636 are on a polar basis.

Signals transmitted from the repeater at the polar receiving repeater oce and received by receive relay 6I6 are repeated on a polar basis as hereinbefore described but are transmitted through wave shaper 64I, resistance 642, winding of receive relay 643 to ground. Relay 643 responds to the polar signals as current and no current impulses of 130 volts and thereby repeats the signals from grounded negative 48- volt battery 644 and ground `connection 646. The signals are repeated to a hub circuit over conductor 645.

Figure 7A In Fig. 7A is shown a modication of the trunk termination at the polar receiving repeater oliice whereby the trunk circuit is connected to multiple jacks for inverse neutral, or hub, circuit'operation at 48 volts. Polarized send relay 12| is normally held in its marking position as shown by biasing current flowing through its lower winding and relay 12| normally transmits over conductor 122', through the noise suppressor and equalizing network to trunk conductor H9 a marking signal. When a spacing signal is received from the hub circuit over the upper spring member of jack 123 by the application of ground in the cord circuit of plug 12d, relay 12| operates to its alternate, or spacing, position due to line current flowing in its upper winding. Relay 12|, upon responding to signals received from the hub circuit, repeats the signals on a dilerential basis, in a circuit traceable from grounded positive 13G-volt battery 125 or grounded connection 126 and their respectively associated spacing and marking contacts and armature of the relay, conductor 122, noise suppressor and equalizing network to trunk conductor 1I9.

Signals received from the polar sending repeater office over trunk conductor 615 are on a one-way polar basis and are repeated by receive relay '19| on a polar basis in a circuit extending from grounded positive 48-vo1t battery 121 and grounded negative Llf8volt battery 128, their respectively associated spacing and marking contacts and armature of relay 1l, over conductors 1&4 and 129, resistance 130, wave shaper 13|, f'

through the winding of polarized receive relay 132 to ground. Relay 132 operates and-repeats the signals as curren and no current impulses, in the circuit extending from grounded negative lS-volt battery 133 and ground connection 131i, their respectively associated marking and spacing contacts and armature of relay 132, conductor 135 to a hub circuit associated with the opposite end of the cord circuit associated with plug 124.

What is claimed is:

1. In a telegraph transmissionsystem, the combination of a polar sending-differentialreceiving repeater circuit, a polar receiving-differential-sending repeater circuit, circuits interconnecting said repeater circuits, sending means at each of said repeater circuits for transmitting signal impulses to the other of said repeater circuits over separate circuits of said interconnecting circuits, and receiving means at each of said other repeater circuits for receiving said signal impulses.

2. In a telegraph transmision system, the combination of a polar sending-diierential-receiving repeater circuit, a polar receiving-differentialsending repeater circuit, circuits interconnecting said repeater circuits, sending means at each of said repeater circuits Afor transmitting signal pulses to the other of said repeater circuits over separate circuits of said interconnecting circuits, receiving means at each of said other repeater circuits for receiving said signal impulses and a ground potential balancing conductor common to the relays of said repeater circuits.

3. In a telegraph transmission system, the combination of a polar sending-diierential-receiving repeater circuit, a polar receiving-diiierential-sending repeater circuit, circuits interconnecting said repeater circuits, sending means at each of said repeater circuits for transmitting signal impulses tothe other of said repeater circuits over a separate one of said interconnectingv circuits, receiving means at each of said other repeater circuits for receiving said signal impulses, and means common to said interconnecting circuits for neutralizing the effect of voltage yinterference induced in either ofA said interconnecting circuits during transmission of signal impulses in either direction.

4. In a telegraph transmission system, the combination of a polar sending-dinerential-receivng repeater circuit, a polar receiving-difierential-sending repeater circuit, circuits interconnecting said repeater circuits, sending means in each of said repeater circuits for transmitting signal impulses to the other oi said repeater circuits over a separate one of said interconnecting circuits, receiving means in each of said other repeater circuits for receiving said signal impulses, and other means at ,the sending end of Veach of said interconnecting circuits for shaping signal impulses outgoing over said interconnecting circuit, said means comprising a diierentially wound retardation coil, one of said windings on said coil including the interconnecting circuit and the other including an artificial line to ground.

5. In a ,telegraph transmission system, the combination of a polar sending-differential-receiving circuit, a polar receiving-diierentialsending repeater circuit, circuits interconnecting said repeater circuits, sending means in each of said repeater circuits for transmitting signal impulses to the other of said repeater circuits over a separate one of said intercommunicating circuits, receiving means in each of said other repeater circuits for receiving said signal impulses, another circuit interconnecting the receiving means of said repeater circuit and a plurality of adjustable impedances connected to one of the nrst-mentioned interconnecting circuits and said other interconnecting circuits for effecting a balance of impedance in said system.

6. In a telegraph transmission system, the combination of a polar sending-differential-receiving repeater circuit, a polar receiving-dinerential-sending repeater circuit, circuits interconnecting said repeater circuits, terminating circuits respectively adapted at one end Afor connecting to each of said repeater circuits and respectively arranged at the other end for connection to a toll line subscribers circuit, a local subscribers station loop, and an inverse neutral circuit.

7. In a telegraph transmission system, the combination of a polar sending-difEerential-receiving repeater circuit, a polar receiving-differential-sending repeater circuit, circuits interconnecting said repeater circuits, each of said repeater circuits comprising a sending device, a`

main receiving device, and an auxiliary receiving device, subscribers stations connected to each of said repeater circuits, each of said subscribers stations connected ,to each of said repeater circuits having means for eiecting in conjunction with its associated sending and associated auX- iliary receiving device half duplex operation between any one of said stations connected to one repeater circuit and any one of said stations connected to the other repeater station.

8. In a telegraph transmission system, the combination of a polar sending-diierential-receiving repeater circuit, a polar receiving-differential-sending repeater circuit, circuits interconnecting said repeater circuits, a sending and a receiving device in each of said repeater circuits, terminating circuits respectively connected to the sending and the receiving devices of each of said repeater circuits and cooperating therewith for effecting full duplex operation between said repeater circuits.

9. In a telegraph transmission system, comprising a rst repeater circuit, a second repeater circuit, a first telegraph line for transmitting signal impulses from said first repeater circuit to said second repeater circuit, a second telegraph line for transmitting signal impulses yfrom said second repeater circuit to said rst repeater circuit, two substantially equal sources of voltage of opposite polarities in said rst repeater circuit, transmitting apparatus in said first repeater circuit connected to said iirst telegraph line for alternately connecting said sources of opposite polarities thereto in accordance with the impulses to be transmitted from said first repeater circuit to said second repeater circuit, receiving apparatus in said second repeater circuit connected between said rst telegraph line and ground, a single source of voltage in said second repeater circuit, transmitting apparatus in said second repeater circuit connected to said second transmission line for alternately connecting ground at said single source of voltage and said ground to said second line in accordance with the signal impulses to be transmitted from said second repeater circuit to said rst repeater circuit, receiving apparatus in said first repeater circuit connected between said second line and a source of voltage thereat which is of opposite polarity to that of said single source of voltage in said second repeater circuit, and means for controlling the magnitudes of the current transmitted over said second line so that the transmission thereover is substantially independent of the leakage resistance of said line.

10. In a half duplex operated telegraph transmission system comprising a rst repeater circuit, a second repeater circuit, a first telegraph line for transmitting impulses 1from said rst repeater circuit to said second repeater circuit, `a second telegraph line for transmitting impulses from said second repeater circuit to said first repeater circuit to substantially equal sources of voltage of opposite polarities in said first repeater circuit, transmitting apparatus in said first repeater circuit connected to said first telegraph line for alternately connecting said sources of opposite polarities thereto in accordance with the impulses to be transmitted from said iirst repeater circuit to said second repeater circuit, receiving apparatus in said second repeater circuit connected between said first telegraph line and ground, a single source of voltage in said second repeater circuit, transmitting apparatus in said second repeater circuit Yconnected to said second telegraph line for alternately connecting ground and said single source of voltage to said second line in accordance with the impulses transmitted from said second repeater circuit to said rst repeater circuit, receiving apparatus in said first repeater circuit connected between said second line and the source of voltage thereat which is of opposite polarity to the voltage of said single source at said second repeater circuit, a second receiving apparatus in said rst repeater circuit for reversing the polarities of sig nals repeated by the first-mentioned receiving apparatusin said rst repeater circuit for further transmission, and means for controlling the magnitude of the current transmitted over the second line so that the transmission thereover is substantially independent of the leakage resistance of said line.

l1. In a full duplex operated telegraph transmission system comprising a rst repeater circuit, a second repeater circuit, a iirst telegraph line for transmitting impulses from said rst repeater circuit to said second repeater circuit, a second telegraph line for transmitting impulses from said second repeater circuit to said first repeater circuit, two substantially equal sources of voltage of opposite polarities in said irst repeater circuit, transmitting apparatus in said first repeater circuit connected to said rst telegraph line for alternately connecting said sources of opposite polarities thereto in accordance with the impulses to be transmitted from said first repeater circuit to said second repeater circuit, receiving apparatus in said second repeater circuit connected between said rst telegraph line and ground, a single source of voltage and a ground connection in said second repeater circuit, transmitting apparatus in said second repeater circuit connected to said second telegraph line for alternately connecting ground connection and said single source of voltage to said second line in accordance with the impulses to be transmitted Vfrom said second repeater circuit to said first repeater circuit, receiving apparatus in said rlrst repeater circuit connected between said second line and the source of voltage thereat which is of opposite polarity to that of said single source in said second repeater circuit, and means for controlling the magnitudes of the current transmitter over said second line so that the transmission thereover is substantially independent of the leakage resistance o f said line.

l2. In a full duplex operated telegraph transmission system, in accordance with claim 10, wherein said means is a third line connecting said rst ,repeater `and said second repeater circuit and connected at each .end `to `a winding which is arranged in diierential relation to a winding connected to one `of said telegraph lines, said third line thereby serving to :neutralize the eiTect in said receiving apparatusin each of said repeater circuits of any voltages inducedin said first and said second telegraphlines.

13. In a differential receiving telegraph system for receiving from a distant sending station over a conductor, a main receiving conductor, a receiving relay having a winding in series with said conductor, a ground potential balancing conductor also extending from said distant station, a winding of said relay in series with said balancing conductor, operable means for changing the resistance of said one of said conductors, and means operable coincidently therewith for changing the resistance of the other conductor by a corresponding amount.

CARL A. DAHLBOM. tICHARD B. HEARN. 

